1. Field of the Invention
The present invention relates to a photographic film cassette, and to a lens-fitted photographic film unit using the same. More particularly, the present invention relates to a photographic film cassette which is improved as to its use with a lens-fitted photographic film unit, and to the lens-fitted photographic film unit using the same.
2. Description of the Prior Art
Lens-fitted photographic film units (hereinafter referred to simply as film units) are now on the market, e.g. under the trademark "Fujicolor Quick Snap" (manufactured by Fuji Photo Film Co., Ltd.). Such known film units are a single-use camera preloaded with photographic film strip (hereinafter referred to as film). The film unit has a main body provided with a film supply chamber and a cassette-containing chamber formed on opposite horizontal sides of a taking lens. The unexposed film is wound in a roll in the film supply chamber. An externally rotatable wind-up wheel is coupled with a spool in the cassette contained in the cassette-containing chamber. A user who has purchased the film unit winds the film frame by frame back into the cassette after each exposure. The film unit in its entirety is then forwarded to a photo laboratory after exposure of the film. An operator at the laboratory unloads the film, and subjects it to development and printing. The user receives finished photographs and a negative film but does not receive the film housing of the film unit.
A 135-type photographic film as defined by the International Organization for Standardization (ISO) has a standard number of photographable frames and a length sufficient for such imaging these frames. The prevailing standard provides an allowance of film beyond the length sufficient for the nominal number of exposures, to such an extent that a conventional camera can take with standard film one or two exposures in addition to the standard number of exposures ascribed to the film. To make greatest use of such allowance in the available length of the film, improved film units are now on the market, e.g. under the trademark "Fujicolor Quick Snap Econoshot" (manufactured by Fuji Photo Film Co., Ltd.), with which a user can take a greater number of photographs than the stated number of photographable frames of the strip of film contained therein, e.g. 27 photographs on a 24-exposure film.
To take good photographs greater in number than the stated number of exposures on the film, it is necessary to position the film initially relative to the exposure aperture of the film unit, so as to keep unchanged the interval between the first frame on the film and the film end attached to the spool in the cassette. This is because, should the interval between the first frame and the film end be too long, it may happen that a predetermined greater number of photographs, e.g. 27, cannot all be taken.
To insert the film cassette into the cassette-containing chamber, it is necessary to engage the spool of the cassette with a drive shaft formed on the wind-up wheel of the film unit. The conventional spool is provided with a key structure formed at an upper end of the spool and shaped in rotational symmetry about 180 degrees or half a rotation. The conventional drive shaft on the wind-up wheel is provided with a fork structure shaped in rotational symmetry about 180 degrees. It may happen that either of the spool and the drive shaft must be rotated relatively through as much as 180 degrees before the spool can be engaged with the drive shaft.
When the film is inserted and positioned in the exposure aperture, the shutter mechanism is set to have a predetermined orientation. This is because even operations in factory associated with assembly, e.g. testing of the shutter mechanism, never consume any extra portion of the film.
When the film is wound up back into the cassette, it rotates a driven sprocket wheel which engages perforations in the film, and this causes a wind-up stop mechanism to prevent the wind-up wheel from rotating further than is necessary to rewind the film by one frame. When the shutter mechanism is kept oriented in consideration of positioning of the film, correspondingly the sprocket wheel is kept positioned rotationally. In further correspondence with this, the wind-up stop mechanism, and the wind-up wheel are kept positioned rotationally. Because of the key structure of the spool, it is impossible when positioning the film to adjust the rotational position of the wind-up wheel as preferred. Accordingly the direction of the key structure of the spool requires adjustment in view of the rotational position of the wind-up wheel.
Prior to inserting the film into the film housing in the course of manufacturing the film unit, nearly all the strip of the film is drawn out of the cassette. Drawing out of the film is terminated before tension along the film increases excessively between the roll and the cassette. This is because, should the tension become excessive while the film is fully drawn out of the cassette, this tension would pull and stretch the film, or curl the film in the direction along the film width, thereby to cause difficulties in positioning the film inside the film unit.
However, reduced tension of the film in the course of insertion frequently causes some deviation in the rotational positions of the spools in the mass production of the film units. As it may happen that the conventional spool must be rotated at 180 degrees relative to the drive shaft before the spool can be engaged with the drive shaft, it frequently happens that a rotational position of the spool is such that the key structure of the spool cannot be engaged with the fork of the wind-up wheel. If the spool is rotated through an angle up to 180 degrees for adjustment according to the fork, the precision of positioning of the film initially relative to the exposure aperture is reduced. The interval between the first frame and the film end will vary. As a result, a predetermined number of photographs, greater than the stated number of exposures on the film, cannot be taken completely.